Devices having a multilayered structure have been widely used as electronic devices. Each layer of the multilayered device may be a functional layer for performing a special function for the device. For example, referring to FIG. 1, an organic light emitting device (OLED) 10 is fabricated by forming a hole injection layer (not shown), a hole transport layer (not shown), an emitting layer 120, an electron transport layer 120, and an electron injection layer 130 between an anode 110 and a cathode 140. Each functional layer may be consisted of an organic and/or inorganic material(s) suitable for performing respective special function. OLED can be significantly improved in terms of I-V characteristics, luminescence efficiency, and operating lifetime by inserting such functional layers between the anode and the emitting layer, and between the emitting layer and the cathode.
In a case of a small molecule type OLED, indium tin oxide may be generally employed for the anode, and copper phthalocyanine (CuPC) may be generally employed for the hole injection layer, and N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPB) may generally be employed for the hole transport layer, and tris-(8-hydroxyquinoline)aluminum (Alq3) may be generally employed for the emitting layer. Alq3 may also be employed for the electron transport layer. Other materials may be employed for each of the functional layers. As the electron injection layer, any one selected from the group comprising LiF, CsF, NaF, NaCl, etc., may be employed. As the cathode, any one selected from the group comprising Al, Ca, Mg, Ag, etc., and their compounds may be employed. In order to improve the luminescence efficiency and the operating lifetime, the thickness of the electron injection layer, for example LiF, may be selected from the optimal range near approximately 10 Å. When the nominal thickness of LiF is about 10 Å, the coverage of LiF on the Alq3 was evaluated to be approximately 66% as will be discussed later.
According to a conventional technique, the coverage of LiF on Alq3 has been estimated by means of atomic force microscopy (AFM), which involves calculating the ratio of the covered area with LiF on Alq3 to the total surface area of Alq3. According to another conventional technique, the coverage of LiF on Alq3 has been estimated by means of X-ray Photoemission Spectroscopy (XPS), which involves analyzing and identifying the chemical elements along the depth profile of the OLED. However, such conventional techniques are complicated in views of measurement and analysis, and require a long time to get the coverage. Further, the conventional techniques involve destructing the sample during the measurement process.